A device for pressurizing a material to be pressed at a target load is well known, wherein the device has a mechanism that uses a servomotor and a load detector. The mechanism feeds the load detected by the detector back to the servomotor, and controls the material to be pressed at a target load (e.g., Patent Documents 1 and 2).
However, by the device for pressurizing disclosed in Patent Documents 1 and 2, because of any improper inputting of a program or a mistake in operating the device, when a rod of an electric cylinder is driven the rod may unexpectedly bump a material to be pressed. The unexpected bump causes an overload, and thus the electric cylinder or a load detector attached to the rod can be broken by being overloaded.
Therefore, for a toggle-type punch press device that has a servomotor as a driving source, a malfunction detector, etc., for the device, is proposed. The detector detects an unexpected abnormal load of the device by the torque of the servomotor and outputs an alarm signal when an unexpected bump occurs so as to avoid the possible overload caused by the bump (e.g., Patent Document 3).
Also, a method is proposed for a servo press device that is operated in a speed-control mode in which an analog voltage is used as an output signal from a means for a command process for a servomotor (servo controller) to a means for providing the command for the servomotor (servo amplifier). The method detects an unexpected abnormal load, outputs an alarm signal for avoiding an overload caused by an unexpected bump, and then a press means is driven in the reverse direction to that for pressurizing (e.g., Patent Document 4).
Patent Document 1: Japanese Patent Publication Laid-open No. 2005-138110
Patent Document 2: Japanese Patent Publication Laid-open No. 2009-101419
Patent Document 3: Japanese Patent Publication Laid-open No. H08-103898
Patent Document 4: Japanese Patent Publication Laid-open No. H11-58099